Heating water with (not for) coffee.

Was not sure exactly where to put this because it could fit many categories.  I work at a very large coffee producer. In the grinding process there is some loss in the transfer system and whole roasted beans get knocked off the end. Its a fractional percentage but when you process 60-70,000lbs of coffee a day probably somewhere around a 55 gallon trashcan of beans is made per day. This can't really be used for anything as it is commingled flavors and roast profiles so it just gets sent to a local commercial composter. I could probably get my hands on some if I asked the right person for permission. So then what to do with it... I have done a little experimenting mixing it up to 20% with peacoal in an automatic stoker type coal stove. Seems to burn ok but I only did it once or twice I am afraid of backdraft burning up into the hopper at higher concentrations and also of gumming up the stove with tars and oils it wasn't designed to deal with. Anthracite coal burns very cleanly. I think it would be better to test it in a multi-fuel or corn stove but I don't have one at my disposal. Also its hard to tell BTU output or burn time vs the straight coal because the stove is fully automatic and ramps up and down based on thermostat demand (for those unfamiliar with stoker coal stoves its basically a pellet stove for coal fill the hopper and forget about it).

Anyway I would really like to heat water for radiant floor heat.
I have thought about trying to adapt a rocket with a similar set up as some have done for burning pellets in a rocket.

Another option I thought about is to make woodgas (coffeegas?) from a downdraft FEMA style gasifier and make some sort of stove type burner for that.

If anyone has other ideas about the best uses of this "fuel source" I am all ears.

The way I see it, its basically a very low moisture content fairly uniform high BTU solid fuel source.

Normally it would be incredibly cost prohibitive as a heating or cooking fuel so very little research I can found has been done. A few studies of using dryed spent grounds from coffee shops but nothing on whole bean I have seen. I have also done some experimenting with fresh (unbrewed) grounds. I packed them into thick cardboard tubes with about 5-8 tons of force from an arbor press creating "coffee logs" which I burned in my cookstove as they were a perfect length for the small firebox. These actually preformed very well but are very labor and time intensive to make as well as messy and would not be at all feasible to make say 3-5 cord of "coffee logs" for the years heating.

I would look more into the process like steam engines, as you know that the coffee is an efficient fuel source.  I don't think that the gasses off of a coffee bean would contain the volatile components that wood releases when biochar is made.  

I think it would be worth trying the spent grounds in a pelletizer. If you could turn the spent grounds into pellets, they could at least function in equipment designed to burn pelletized material. You might have to tinker with either the formulation of a binding agent that perhaps oxidizes the pellet in combustion, or is an accelerant, or perhaps with the airflow on the stove, but the spent grounds would at least be in a convenient format to handle and combust with conventional equipment.

-CK

I don't think that the gasses off of a coffee bean would contain the volatile components that wood releases when biochar is made.  

Correct me if I am wrong but the way I understand it most any dry readily burnable biomass produces syngas when put through a gasifier pyrolysis process.

I forgot to mention another option I thought of which is composting it directly in a methane digester for biogas. I know coffee produces rich compost but I am unsure of how quickly this happens or how readily it happens if you were composting 100% coffee rather than as a mix with other organics. (high acidity)

If they produce biogas, then you could do both. I have been tinkering with this design strategy that is essentially a rocket stove, but there's a canister that can be loaded with a fuel source like wood, so the gases can be captured. I have seen wood gas pumped into a propane tank using a tire compressor. My idea is to pipe a small bit of wood gas back into a propane bar at the beginning of the rocket stove that heats the canister to create more biogas.

You would of course need to burn wood in the rocket stove (in addition to the wood gas burner), because you need the wood gas inside the rocket stove to combust inside the reburn chamber.  While capturing wood gas from the reburn chamber is a dirty idea, using the rocket stove heat to make bio gas from your coffee is a good solution.  The canister then produces a high quality char coal, and you can bottle the biogas.

There's a YouTube video of a guy capturing wood gas using a paint can with a brake line attached into the middle of the lid. The then filtered and captured the gas using water. This also let him pressurize the gas using water. If you can find the video, he uses aquariums to hold the water. It would be a resource of info for you.

It is my understanding woodgas (syngas) does not compress well and is unfeasible on the home scale.

https://itstillruns.com/can-gas-compressed-stored-tank-7977114.html here is a quick rundown of why but much more complicated explanations can be found with a little research. Woodgas is seen as an energy source to use as it is produced which is why it likens itself well the use of running engines.

Another word of caution, if you do want to play with compressing woodgas despite the mathmatics you need to make very sure your process is able to compress it in the full absence of oxygen. Otherwise you have just created a high pressure explosive gas bomb. The reason for instance a gas BBQ grill doesn't burn back up the hose and explode the tank is there is no oxygen in the line to make combustion possible. Change that equation to a quantity of oxygen sufficient for combustion and you will have a dangerous problem at hand.

Chris Kott wrote:I think it would be worth trying the spent grounds in a pelletizer. If you could turn the spent grounds into pellets, they could at least function in equipment designed to burn pelletized material. You might have to tinker with either the formulation of a binding agent that perhaps oxidizes the pellet in combustion, or is an accelerant, or perhaps with the airflow on the stove, but the spent grounds would at least be in a convenient format to handle and combust with conventional equipment.

-CK

The home scale pelletizers I have seen seem to be incredibly slow and inefficient. from the Videos I have seen on youtube I cant imagine someone producing the 3 to 5 tons most people in my neck of the woods use per winter with such a unit. Maybe if you wanted to make some for a pellet grill or some other very limited use...And the commercial scale ones are well, commercial scale in size and price.

I do think a pellet stove or more likely a multifuel stove designed to burn corn and pellets and sometimes pits would readily burn whole bean, but I don't have one and they are not cheap even used. And no one I know wants me gumming theirs up with experimenting. But the main drawback is they require electric input so if the power is out there is no heat. (this is one of the many reasons I heat primarily with wood currently)

I might go in a different direction...

Coffee composts really well, so if you made a compost with all your coffee beans, I think you could make a Jean Pain type of compost pile and heat water via that way. It would be only too 140 degrees or so, but jeesh that mush have some use. It would be very simple to set up and you end up with excellent compost. Kind of a two-fer!

I would be amazed if burning coffee (or any biomass for that matter) produced any more tars than the combustion of heavy hydrocarbons normally found in coal.

As you can see from my details I live in a country where there is a lot of coffee production, and I can tell you from experience two things:

One of the largest producers of instant coffee in this country produces part of their process steam by burning up the spent coffee grounds (after extracting the coffee extract which is then spray dried) in a boiler.

Coffee husks (I know, not exactly coffee grounds) make fantastic fuel and I've seen it used (first hand) in kilns to produce clay bricks, completely replacing coal with virtually no particulate emissions or ash formation.